Phenolic polymers and photoresists comprising same

ABSTRACT

The present invention relates to new polymers that contain phenolic groups spaced from a polymer backbone and photoacid-labile group. Preferred polymers of the invention are useful as a component of chemically-amplified positive-acting resists.

The present invention relates to new phenolic copolymers that comprise aphotoacid-labile groups and a distinct phenolic that is spaced from thecopolymer such as through a polymerized acrylate moiety. Polymers of theinvention are particularly useful as a component of chemically-amplifiedpositive-acting resists.

Photoresists are photosensitive films used for transfer of images to asubstrate. A coating layer of a photoresist is formed on a substrate andthe photoresist layer is then exposed through a photomask to a source ofactivating radiation. The photomask has areas that are opaque toactivating radiation and other areas that are transparent to activatingradiation. Exposure to activating radiation provides a photoinducedchemical transformation of the photoresist coating to thereby transferthe pattern of the photomask to the photoresist-coated substrate.Following exposure, the photoresist is developed to provide a reliefimage that permits selective processing of a substrate.

Chemically-amplified-type resists have been increasingly employed,particularly for formation of sub-micron images and other highperformance applications. Such photoresists may be negative-acting orpositive-acting and generally include many crosslinking events (in thecase of a negative-acting resist) or deprotection reactions (in the caseof a positive-acting resist) per unit of photogenerated acid. In thecase of positive chemically-amplified resists, certain cationicphotoinitiators have been used to induce cleavage of certain “blocking”groups pendant from a photoresist binder, or cleavage of certain groupsthat comprise a photoresist binder backbone.

While currently available photoresists are suitable for manyapplications, current resists also can exhibit significant shortcomings,particularly in high performance applications such as formation ofhighly resolved sub-half micron and sub-quarter micron features.

Consequently, photoresists are of interest that can be photoimaged withshort wavelength radiation, including exposure radiation of 270 nm orless, such as wavelengths of 248 nm (provided by KrF laser). SeeJP1996044063 which reports a certain resist exposed with a KrF stepper.Use of such short exposure wavelengths can enable formation of smallerfeatures. Accordingly, a photoresist that yields well-resolved imagesupon 248 nm exposure could enable formation of extremely small (e.g.sub-0.25 μm) features that respond to constant industry demands forsmaller dimension circuit patterns, e.g. to provide greater circuitdensity and enhanced device performance.

It thus would be desirable to have new photoresist compositions,particularly resist compositions that can be imaged at short wavelengthssuch as 248 nm.

We have now found new phenolic polymers that contain photoacid-labileunits and phenolic groups that are spaced by at least carbon or otheratom from the polymer backbone.

Particularly preferred polymers of the invention comprise polymerizedacrylate groups that comprise a phenolic moiety spaced from the polymerbackbone.

In one aspect, polymers and photoresists comprising such polymers areprovided where the polymer comprises repeat units that comprise astructure of the following Formula I:

wherein in Formula I, Z is a bridge unit; X is one or more atoms; eachR¹ is the same or different non-hydrogen substituent; and m is aninteger of from zero (where no R¹ substituents are present) to 4.

In certain preferred aspects of the invention, polymers and photoresistscomprising such polymers are provided where the polymer comprises repeatunits that comprise a structure of the following formula II:

where R is hydrogen or alkyl such as C₁₋₆alkyl particularly methyl; andX, R¹ and m are the same as defined for Formula I above.

Preferred polymers and photoresists comprising such polymers maycomprise additional repeat units distinct from spaced phenolic unitssuch as those of Formulae I and II above, i.e. preferred polymers of theinvention include copolymers, terpolymers, tetrapolymers, pentapolymersand other higher order polymers, with terpolymers and tetrapolymersbeing particularly suitable for many photoresist applications.

Generally preferred higher order polymers may comprise repeat units thatmay facilitate lithographic processing of a photoresist comprising thepolymer. Thus, preferred additional polymer repeat unitsphotoacid-labile groups such as those that can generate an alkaline,aqueous-soluble group such as carboxy in the presence of photogeneratedacid; groups that may be substantially inert to lithographic processingsuch as phenyl optionally substituted with ring substituents that do notundergo cleavage reactions under typical lithographic conditions such ashalogen, optionally substituted alkyl including C₁₋₆alkyl, andoptionally substituted alkoxy including C₁₋₆alkoxy; cyano-containinggroups.

More particularly, preferred higher order polymers of the invention maycontain photoacid-labile groups in addition to spaced phenolic groupswith additional distinct repeat units optionally present. For instance,preferred polymers of the invention include those that comprise astructure of the following Formula III:

wherein each Z is the same or different bridge unit; X, R¹ and m are thesame as defined in Formula I above;

AL is a moiety that comprises a photoacid-labile group such as aphotoacid-labile ester or acetal group;

Y is a moiety that is distinct from the spaced phenolic group or moietythat comprises AL, e.g. suitable Y groups may comprise moieties that aresubstantially unreactive to lithographic processing e.g. such as phenyloptionally substituted with moieties that are substantially inert tolithographic processing such as halogen, cyano, alkyl, alkoxy; estergroups that do not undergo photoacid-induced cleavage reactions;alicyclic groups having such as groups having 5-20 ring carbon atomse.g. cylohexyl, adamantly, norbornyl; and lactones such asbutyrolacontes;

a, b and c are mole percents of the respective polymer units based ontotal repeat units in the polymer and a and b are each greater than zeroand c may be zero (where no Y groups are present in the polymer) orgreater than zero. Preferred values of a are from 5 to about 95 or morepercent, more typically from about 10 to about 40, 50, 60, 70, 80 or 90percent; preferred values of b are from about 1 to about 70 percent,more preferably from about 2, 3, 4, or 5 to about 10, 15, 20, 25, 30, 40or 50 percent; preferred values of c are from zero, 1, 2, 5, 10 or 15 toabout 20, 25, 30, 40, 50 or 60 percent, more typically about 5 or 10 toabout 15, 20, 25 or 30 percent.

In one aspect, preferred polymers of the invention comprisephotoacid-labile ester groups in addition to spaced phenolic groups. Forinstance, such preferred polymers comprise a structure of the followingFormula IV:

wherein X, R¹, m, Y, a, b and c are each the same as defined in FormulaIII above;

each R is the same or different and is hydrogen or optionallysubstituted alkyl such as optionally substituted C₁₋₆ alkyl particularlymethyl; and

P is a moiety that provides a photoacid-labile ester, particularly whereP provides a fully-substituted alkyl atom linked to the ester oxygensuch as tert-butyl and methyladamantyl.

Preferred polymers of the invention can be highly useful as a resincomponent of a photoresist composition. Resists of the inventiontypically contain a photoactive component such as one or more photoacidgenerator compounds in addition to the resin component. Photoresists ofthe invention also may contain a blend of resins, where at least oneresin blend member is a polymer of the invention. Preferred photoresistsare chemically-amplified resists where a polymer of the invention and/oranother component of the resists such as an additional resin whichcomprises one or more photoacid-labile groups.

The invention also provides methods for forming relief images, includingmethods for forming a highly resolved relief image such as a pattern oflines where each line has essentially vertical sidewalls and a linewidth of 0.40 microns or less, and even a width of 0.25, 0.20 or 0.16microns or less. The invention further provides articles of manufacturecomprising substrates such as a microelectronic wafer substrate orliquid crystal display or other flat panel display substrate havingcoated thereon a polymer, photoresist or resist relief image of theinvention. The invention also includes methods for manufacturing sucharticles, particularly semiconductor chips, using a photoresist and/orpolymer of the invention.

Additionally, in a preferred aspect, the invention provides improved ionimplantation processing. Such a process may include implanting dopantions (e.g. Group III and/or V ions such as boron, arsenic, phosphorusand the like) into a surface of a substrate (e.g. semiconductor wafer)having thereon a photoresist of the invention which serves as a mask.The resist-masked substrate may be placed in a reaction chamber whichcan provide reduced pressure and a plasma of ions from an ionizablesource. Those ions include dopants which are electrically active whenimplanted into the substrate. Voltages may be applied in the reactionchamber (such as through electrically conductive chamber walls) toselectively implant the dopant ions.

Other aspects of the invention are disclosed infra.

As stated above, polymers are provided that comprise phenolic groupsspaced by one or more atoms from the polymer backbone. Typical spacergroups may comprise alkyl and/or hetero atoms such as oxygen oroptionally substituted sulfur (e.g. S(O), S(O)₂) that comprise a chainof 1 or more atoms, generally 1 to about 2, 3, 4, 5, 6, 7, 8, 9, or 10atoms, interposed between the polymer backbone and a phenolic group.Polymers of the invention are particularly useful as a photoresist resincomponent.

Polymers of the invention also may contain units in addition to spacedphenolic groups. As discussed above, preferred polymers comprise repeatunits that contain one or more photoacid-labile groups.

Suitable photoacid-labile groups include ester and acetal groups.Preferred are t-butyl esters as well as carbon alicyclic photoacidlabile ester groups. Preferred alicyclic groups of such esters will havea molecular volume of at least about 125 or about 130 Å³, morepreferably a molecular volume of at least about 140 or 160 Å³. Alicyclicgroups larger than about 220 or 250 Å³ may be less preferred, in atleast some applications. References herein to molecular volumesdesignate volumetric size as determined by standard computer modeling,which provides optimized chemical bond lengths and angles. A preferredcomputer program for determining molecular volume as referred to hereinis Alchemy 2000, available from Tripos. For a further discussion ofcomputer-based determination of molecular size, see T Omote et al,Polymers for Advanced Technologies, volume 4, pp. 277-287.

Particularly preferred quaternary alicyclic groups of photoacid-labileunits include the following, where the wavy line depicts a bond to thecarboxyl oxygen of the ester group, and R is suitably optionallysubstituted alkyl, particularly C₁₋₈ alkyl such as methyl, ethyl, etc.

Suitable photoacid-labile acetal groups may be provided by reaction of avinyl ether such as ethyl vinyl ether with a hydroxy or carboxy group.

In this regard, photoacid-labile groups also may be grafted onto othermonomers, or a preformed polymer. For example, photoacid-labile estersand acetal moieties may be suitably grafted onto phenolic —OH groups ofa formed resin or a phenolic monomer. For instance, an ester graftedonto a hydroxy group is a preferred acid-labile group (de-esterificationoccurs in the presence of photogenerated acid to providedeveloper-solublizing carboxy group). Such esters may be provided e.g.by reaction of a haloacetate compound (e.g. tert-butyl chloroacetate)with a phenolic hydroxy group. Acetal groups also are preferredphotoacid-labile groups; for example a vinyl ether compound may begrafted onto a phenolic hydroxy moiety to provide a photoacid-labileacetal group. Suitable vinyl ether reagents to provide aphotoacid-labile acetal group include compounds having at least one—(CH═CH)—O— group such as ethylvinyl ether and the like.

Polymers of the invention also may comprise other groups in addition oralternative to photoacid-labile groups. For example, dissolutionenhancers may be included in a polymer of the invention, such asanhydrides and lactones. Suitable anhydrides include e.g. polymerizedunits that comprise maleic anhydride and/or itaconic anhydride. Suitablelactone groups include e.g. butyrolactone moieties. Contrast enhancinggroups also may be present in polymers of the invention, such as groupsprovided by polymermization of methacrylic acid, acrylic acid, and suchgroups protected with photoacid labile groups e.g. ethoxyethylmethacrylate, t-butoxy methacrylate, and t-butylmethacrylate. Asdiscussed above, groups that are essentially inert to photolithographyalso may be employed, such as carbocyclic aryl groups, particularlyphenyl groups, which may be provided by reaction of styrene, and phenylor other aryl groups that are optionally substituted by moieties thatare essentially unreactive to thermal (e.g. between 150 to 200° C.) andphotoacid conditions of photolithography.

In certain aspects of the invention, polymers that comprises polymerizedacrylate groups are provided. References herein to an acrylate compoundor polymer includes substituted acrylates such as a methacrylate.Phenolic/acrylate copolymers and higher order polymers such asterpolymers and tetrapolymers are particularly preferred. One or morepolymer repeat units may comprise polymerized acrylate groups, includingthe spaced phenolic unit and/or unit(s) that comprise photoacid-labilemoieties.

Suitably polymers of the invention contains from 30 to 90 mole percentphenolic units, more preferably 40 to 60 mole percent phenolic units.Polymers that contain non-phenolic (no hydroxy or carboxy substitution)phenyl units suitably have such units present in an amount of from 3 to30 or 40 mole percent based on total polymer units, preferably from 5 to10, 15 or 20 mole percent based on total polymer units.

As discussed, various moieties described herein, including moieties ofpolymers of the above formulae may be optionally substituted. A“substituted” group may be substituted at one or more availablepositions, typically 1, 2, or 3 positions by one or more suitable groupssuch as e.g. halogen (particularly F, Cl or Br); cyano; nitro; C₁₋₆alkylsulfonyl such as mesyl; C₁₋₈ alkyl; C₁₋₈ alkoxy; C₂₋₈ alkenyl; C₂₋₈alkynyl; hydroxyl; alkanoyl such as a C₁₋₆ alkanoyl e.g. acyl.

Polymer Syntheses

Polymers of the invention can be prepared by a variety of methods.

A variety of monomers having a spaced phenolic moiety are commerciallyavailable. Suitable monomers also may be readily synthesized. Forexample, a hydroquinone compound and an acrylic acid anhydride may bereacted under acidic conditions to provide a spaced phenolic acrylatecompound. See, for instance, the procedures of Example 1 which follows,which yields hydroxyphenylmethacrylate.

More particularly, suitable monomers can be produced as shown in thefollowing Scheme 1:

As outlined in the exemplary Scheme 1, reaction of a polyhydroxy phenylcompound such as hydroquinone 1 shown in Scheme 1 with a vinyl acidanhydride 2 in the presence of acid can provides a phenolic methacrylatecompound 3. In Scheme 1 above, the depicted “R” is the same as definedin Formula (I) above. A particularly preferred synthesis of Scheme 1 isexemplified in Example 1 below.

As outlined in the exemplary Scheme 2, a vinyl acid anhydride can beemployed as reagent 2 in Scheme 1 above. More particularly, an acrylateacid 4 can be reacted with an acid anhydride 5, preferably in thepresence of a further acid to provide a vinyl acid anhydride 6 to yielda phenolic methacrylate compound 3. In Scheme 2 above, the depicted “R”is the same as defined in Formula (I) above. A particularly preferredsynthesis of Scheme 2 is exemplified in Example 2 below.

As outlined in the above exemplary Scheme 3, polyhydroxy compound 7 canbe reacted with an acid anhydride 8 preferably in the presence of acidto provide mono-ester phenolic intermediate 9. If desired, excessstarting materials may be recovered, and compound 9 is then reacted withacrylate acid 10 preferably in the presence of a further acid to providephenolic methacrylate compound 11. In Scheme 3 above, the depicted “R”is the same as defined in Formula (I) above. A particularly preferredsynthesis of Scheme 3 is exemplified in Example 3 below.

The two-step process outlined in Scheme 3 can provide several notableadvantages including use of comparatively inexpensive reagents (e.g.,Ac₂O). Additionally, the process of Scheme 3 can facilitate synthesis ofthe acrylate compound 11, i.e. where R of compound 11 is hydrogen.

Particularly preferred monomers that may be employed to form a polymerof the invention include those of the following Formula V:

wherein R, R¹ and m are as defined in Formula I through IV above.

Acrylates are especially preferred monomers to employ to produce apolymer of the invention, such as compounds of the following Formula VI:

wherein R is hydrogen or optionally substituted alkyl such as optionallysubstituted C₁₋₆alkyl, and R is preferably hydrogen or methyl

Polymers of the invention may be suitably formed by an addition reactionwhich may include free radical polymerization, e.g., by reaction ofselected monomers (one of which includes a spaced phenolic group) toprovide the various units as discussed above in the presence of aradical initiator under an inert atmosphere (e.g., N₂ or argon) and atelevated temperatures such as 70° C. or greater, although reactiontemperatures may vary depending on the reactivity of the particularreagents employed and the boiling point of the reaction solvent (if asolvent is employed). Suitable reaction solvents include e.g.tetrahydrofuran and ethyl lactate. Suitable reaction temperatures forany particular system can be readily determined empirically by thoseskilled in the art based on the present disclosure. A variety of freeradical initiators may be employed. For example, azo compounds may beemployed such as azo-bis-2,4-dimethylpentanenitrile. Peroxides,peresters, peracids and persulfates also could be employed. See Examples4 and 7 which follow for exemplary reagents and reaction conditions.

Suitable monomers for reaction to provide polymers of the inventioninclude optionally substituted vinyl phenyl, optionally substitutedstyrene, optionally substituted alpha-methyl styrene, methacrylonitrile,acrylonitrile, 2-methyladamantylmethacrylate, 2-methyladamantylacrylate,or an alpha-butyrolactone methacrylate.

Other monomers that can be reacted to provide a polymer of the inventioncan be identified by those skilled in the art. For example, to provideacid labile groups, corresponding monomers can be reacted such ast-butymethacrylate, t-butylacrylate, t-butoxy methacrylate,t-butylmethacrylate; and ethoxyethyl methacrylate; to provide pendantacid groups corresponding monomers acid monomers can be reacted such asmethacrylic acid and acrylic acid; and dissolution enhancers such asanhydrides which may be provided by reaction of suitable monomers suchas itaconic anhydride and maleic anhydride.

Polymers of the invention suitably may have a wide ranges of molecularweights and molecular weight distributions. For instance, a polymer ofthe invention suitably may have a weight average molecular weight(M_(w)) of 1,000 to 100,000, more preferably 2,000 to 30,000, still morepreferably from 2,000 to 15,000 or 20,000, with a molecular weightdistribution (M_(w)/M_(n)) of 3 or less, more preferably a molecularweight distribution of 2 or less. Molecular weights (either M_(w) orM_(n)) of the polymers of the invention are suitably determined by gelpermeation chromatography.

Photoresist Compositions

As discussed above, further provided are photoresist compositions thatcomprise a resin component that contains a resin with spaced phenolicgroups.

The photoresist compositions of the invention can provide highlyresolved relief images upon exposure to short wavelengths, particularly248 nm. Photoresists of the invention preferably arechemically-amplified positive resists, which utilize photoacid-inducedcleavage of pendant alkyl ester or acetal polymer groups to providesolubility differentials between exposed and unexposed areas of a resistcoating layer.

Polymers of the invention used in photoresist formulations shouldcontain a sufficient amount of photogenerated acid labile ester groupsto enable formation of resist relief images as desired. For instance, asuitable amount of such acid labile ester groups will be at least 1 molepercent of total units of the polymer, more preferably 2 to 50 or 60mole percent. See the examples which follow for exemplary preferredpolymers.

As discussed above, resists of the invention may contain one or morepolymers in addition to and distinct from a polymer having spacedphenolic groups. Such additional polymers include those that havephotoacid labile groups that may be deblocked under relatively mildconditions, e.g. a polymer than has acetal groups. Such a furtherpolymer that has acetal groups suitably may be e.g. a phenolic polymer(e.g. a poly(vinylphenol)) that has acetal groups grafted onto thephenolic —OH moieties such as by reaction of the phenolic polymer withether vinyl ether or other vinyl ether.

The amounts of each member of such a resin blend may vary rather widely,e.g. the weight ratio of a polymer having spaced phenolic groupsrelative to a second distinct resin may be 1:10 to 10:1, more preferablya weight ratio of from 2:8 to 8:2.

Photoresists of the invention comprise a photoactive components,preferably one or more photoacid generators (i.e. “PAG”) that aresuitably employed in an amount sufficient to generate a latent image ina coating layer of the resist upon exposure to activating radiation.Suitable photoacid generators include imidosulfonates such as compoundsof the following formula:

wherein R is camphor, adamantane, alkyl (e.g. C₁₋₁₂ alkyl) andperfluoroalkyl such as perfluoro(C₁₋₁₂alkyl), particularlyperfluorooctanesulfonate and perfluorononanesulfonate. A specificallypreferred PAG isN-[(perfluorooctanesulfonyl)oxy]-5-norbornene-2,3-dicarboximide.

Sulfonate compounds are also suitable PAGs for resists overcoated acoating composition of the invention, particularly sulfonate salts. Twosuitable agents for 193 nm and 248 nm imaging are the following PAGS 1and 2:

Such sulfonate compounds can be prepared as disclosed in European PatentApplication 96118111.2 (publication number 0783136), which details thesynthesis of above PAG 1.

Also suitable are the above two iodonium compounds complexed with anionsother than the above-depicted camphorsulfonate groups. In particular,preferred anions include those of the formula RSO₃— where R isadamantane, alkyl (e.g. C₁₋₁₂ alkyl) and perfluoroalkyl such asperfluoro (C₁₋₁₂alkyl), particularly perfluorooctanesulfonate andperfluorobutanesulfonate.

Other known PAGS also may be employed in the resists of the invention.

A preferred optional additive of resists of the invention is an addedbase, particularly tetrabutylammonium hydroxide (TBAH), ortetrabutylammonium lactate, which can enhance resolution of a developedresist relief image. The added base is suitably used in relatively smallamounts, e.g. 0.03 to 5 percent by weight relative to the total solids.

Photoresists of the invention also may contain other optional materials.For example, other optional additives include anti-striation agents,plasticizers, speed enhancers, etc. Such optional additives typicallywill be present in minor concentrations in a photoresist compositionexcept for fillers and dyes which may be present in relatively largeconcentrations, e.g., in amounts of from 5 to 30 percent by weight ofthe total weight of a resist's dry components.

The resists of the invention can be readily prepared by those skilled inthe art. For example, a photoresist composition of the invention can beprepared by dissolving the components of the photoresist in a suitablesolvent such as, for example, ethyl lactate, ethylene glycol monomethylether, ethylene glycol monomethyl ether acetate, propylene glycolmonomethyl ether; propylene glycol monomethyl ether acetate and3-ethoxyethyl propionate. Typically, the solids content of thecomposition varies between 5 and 35 percent by weight of the totalweight of the photoresist composition. The resin binder and photoactivecomponents should be present in amounts sufficient to provide a filmcoating layer and formation of good quality latent and relief images.See the examples which follow for exemplary preferred amounts of resistcomponents.

The compositions of the invention are used in accordance with generallyknown procedures. The liquid coating compositions of the invention areapplied to a substrate such as by spinning, dipping, roller coating orother conventional coating technique. When spin coating, the solidscontent of the coating solution can be adjusted to provide a desiredfilm thickness based upon the specific spinning equipment utilized, theviscosity of the solution, the speed of the spinner and the amount oftime allowed for spinning.

The resist compositions of the invention are suitably applied tosubstrates conventionally used in processes involving coating withphotoresists. For example, the composition may be applied over siliconwafers or silicon wafers coated with silicon dioxide for the productionof microprocessors and other integrated circuit components.Aluminum-aluminum oxide, gallium arsenide, ceramic, quartz, copper andglass substrates are also suitably employed.

The resists and methods of the invention are particularly use in e.g.the manufacture of thin film heads (e.g. 3 to 5 μm), magnetic disks, CDmasks, and back-end implants.

Following coating of the photoresist onto a surface, it is dried byheating to remove the solvent until preferably the photoresist coatingis tack free. Thereafter, it is imaged through a mask in conventionalmanner. The exposure is sufficient to effectively activate thephotoactive component of the photoresist system to produce a patternedimage in the resist coating layer and, more specifically, the exposureenergy typically ranges from 1 to 100 mJ/cm², dependent upon theexposure tool and the components of the photoresist composition.

As discussed above, coating layers of the resist compositions of theinvention are preferably photoactivated by a short exposure wavelength,particularly sub-300 nm exposure wavelengths such as 248 nm. However,the resist compositions of the invention also may be suitably imaged athigher wavelengths. For example, a resin of the invention can beformulated with an appropriate PAG and used as a chemically-amplifiedpositive I-line resist, i.e. a resist imaged at 365 nm. Resists of theinvention also will be useful for exposure with electron beams (E-beamexposure) and extreme-UV exposure (EUV) such as sub-50 nm or sub-20 nmexposure, particularly 13 nm exposure.

Following exposure, the film layer of the composition is preferablybaked at temperatures ranging from 70° C. to 160° C. Thereafter, thefilm is developed. The exposed resist film is rendered positive workingby employing a polar developer, preferably an aqueous based developersuch as quaternary ammonium hydroxide solutions such as a tetra-alkylammonium hydroxide solution; various amine solutions preferably a 0.26 Ntetramethylammonium hydroxide, such as ethyl amine, n-propyl amine,diethyl amine, di-n-propyl amine, triethyl amine, or methyldiethylamine; alcohol amines such as diethanol amine or triethanol amine;cyclic amines such as pyrrole, pyridine, etc. In general, development isin accordance with procedures recognized in the art.

After development and any post-development thermal cure, an ion implantprocess may be conducted, e.g. by bombardment of the substrate withresist relief image with one or more dopant ions such as argon, boron,boron fluoride, arsenic, phosphorus and/or nitrogen, with arsenic,phosphorus and/or boron being more typically employed. The ionimplanting is preferably conducted under high energy conditions, e.g. 20eV or more, such as 40, 50, or 80 eV or more, and preferably underreduced pressure in a chamber.

Thereafter, the developed substrate may be selectively processed onthose areas bared of resist, for example by chemically etching orplating substrate areas bared of resist in accordance with proceduresknown in the art. For the manufacture of microelectronic substrates,e.g., the manufacture of silicon dioxide wafers, suitable etchantsinclude a gas etchant, e.g. a halogen plasma etchant such as a chlorineor fluorine-based etchant such a Cl₂ or CF₄/CHF₃ etchant applied as aplasma stream. After such processing, resist may be removed from theprocessed substrate using known stripping procedures.

As discussed above, photoresists of the invention are particularlyuseful to form metal bumps on a semiconductor wafer. Such processing caninclude: a) disposing on a semiconductor wafer a photoresist of theinvention, preferably to provide a thick film coating layer such as adried resist coating layer of 50 μm or greater; c) imagewise exposingthe layer of photosensitive composition to actinic radiation, includingsub-300 nm radiation particularly 248 nm; d) developing the exposedlayer of photosensitive composition to provide patterned areas; e)depositing a metal into the patterned areas; and f) removing the exposedphotosensitive composition to provide a semiconductor wafer having metalbumps.

In such bump-forming methods, the photoresist layer is imaged so as toform apertures such as vias in the photosensitive layer. In suchprocess, the photosensitive layer is disposed on a conductive layer onthe electronic device. Exposure of the photosensitive composition andsubsequent development provides defined holes (vias) in thephotosensitive composition and exposes the underlying conductive layer.Accordingly, the next step of the process is to deposit metal or metalalloy bumps with the defined holes (vias). Such metal deposition may beby electroless or electrolytic deposition processes. Electrolytic metaldeposition is preferred. In an electrolytic metal deposition process,the electronic device substrate, i.e. semiconductor wafer, functions asthe cathode.

Prior to deposition of a metal or metal alloy, such as that suitable asa solder, a conductive layer such as copper or nickel may be depositedby sputtering, electroless deposition and the like, to form theunder-bump-metal. Such under-bump-metal layer is typically from 1000 to50,000 Å in thickness and acts as a wettable foundation to thesubsequently plated solder bump.

A wide variety of metals may be deposited electrolessly, including, butnot limited to, copper, tin-lead, nickel, gold, silver, palladium, andthe like. Suitable metals and metal alloys that may be depositedelectrolytically include, but are not limited to, copper, tin, tin-lead,nickel, gold, silver, tin-antimony, tin-copper, tin-bismuth, tin-indium,tin-silver, palladium, and the like. Such metal plating baths are wellknown to those skilled in the art and are readily available from avariety of sources.

In one embodiment, the metal deposits on the semiconductor wafer areuseful as solder bumps. Accordingly, it is preferred that the metalbumps are solderable metals and metal alloys, such as tin, tin-lead,tin-copper, tin-silver, tin-bismuth, tin-copper-bismuth,tin-copper-silver, and the like. Suitable metals and metal alloys forsolder bump formation are disclosed in U.S. Pat. Nos. 5,186,383;5,902,472; 5,990,564; 6,099,713; and 6,013,572, as well as EuropeanPatent Application No. EP 1 148 548 (Cheung et al.). Exemplary metalsand metal alloys include, but are not limited to: tin; tin-copper alloyhaving less than 2% wt copper and preferably about 0.7% wt copper; atin-silver alloy having less than 20% wt silver and preferably from 3.5to 10% wt silver; a tin bismuth alloy having from 5 to 25% wt bismuthand preferably about 20% wt bismuth; and a tin-silver-copper alloyhaving less than 5% wt silver and preferably about 3.5% wt silver, lessthan 2% wt copper and preferably about 0.7% wt copper, and the balancebeing tin. In one embodiment, the metal alloys used for solder bumps arelead-free, i.e. they contain ≦10 ppm of lead.

In general, suitable electrolytic metal plating baths are acidic andcontain acid, water a soluble form of the metal or metals to bedeposited and optionally one or more organic additives, such asbrighteners (accelerators), carriers (suppressors), levelers, ductilityenhancers, wetting agents, bath stabilizers (particularly fortin-containing baths), grain refiners and the like. The presence, typeand amount of each optional component varies depending upon theparticular metal plating bath used. Such metal plating baths aregenerally commercially available.

Binary alloys may be deposited from a single bath, as in the case oftin-copper, tin-bismuth, tin-silver, tin-lead and the like, or may bedeposited as individual layers from multiple plating baths and reflowedto form and alloy. Such reflow technique is described in U.S. Pat. No.6,013,572. Such reflow is typically performed after removal of theremaining photosensitive composition.

In such a process, the resist composition functions as a protectivelayer to areas that are not to be plated. Following metal deposition,the remaining resist composition is stripped, such as by using acommercially available N-methylpyrrolidone (“NMP”) based stripper at atemperature of about 40° to 69° C.

The following non-limiting examples are illustrative of the invention.

EXAMPLE 1 Preparation of Methacrylic Acid Anhydride/Methacrylic AcidMixture

Acetic anhydride was added by dropwise addition to an excess ofmethacrylic acid (4:1) while simultaneously distilling acetic anhydridefrom the mixture. The reaction was carried out at 95Oc and 300 mmHg,catalyzed by 1 mole % amberlyst-15 (A-15), and inhibited with 3000 ppmPTZ and 1000 MEHQ pppm, 8% O₂. At the end of the reaction, excessmethacrylic acid was recovered by distillation under reduced pressureand the catalyst was recovered by filtration.

EXAMPLE 2 Monomer Synthesis; Preparation of Hydroxyphenyl Methacrylate

To a mechanically stirred solution of 2 moles of hydroxyquinonedissolved in 3 moles of methacrylic acid at 120° C. and atmosphericpressure was added dropwise (30 min) 1 mole of methylacrylic acidanhydride and the mixture was maintained at 120° C. with stirring foradditional 4 hrs (NMR analysis). Throughout the course of the reaction8% oxygen was admitted to the system. At the end of the reaction, themethacrylic acid was recovered by distillation under reduced pressure(110° C. and 200 mmHg), and the unreacted excess hydroquinone wasprecipitated out by the addition of toluene (1 liter) to the reactionmixture. A low level (1-2%) of the monomer2-methyl-5-methylenehexanedioic acid was formed. This monomer wasseparated from the mixture by a washing step with distilled water. Afterphase separation, the desired 4-hydroxyphenyl methacrylate was obtainedat 97% yield by the distillation of toluene under reduced pressure. {mp.(Uncorrected) 120° C.; Anal. Calcd. For C₁₀H₁₀O₃: C, 67.41: H, 5.66; O,26.94. Found: C, 67.37; H, 5.62}.

EXAMPLE 3 Monomer Synthesis; Preparation of Hydroxyphenyl MethacrylateThrough Mono-Ester Intermediate

A large excess of hydroquinone is reacted with acetic acid anhydride inthe presence of acetic acid to provide the mono-acetate phenoliccompound 1,4-C₆H₄(OH)(OOCCH₃). Excess starting materials are recovered,and the intermediate compound 1,4-C₆H₄(OH)(OOCCH₃) is reacted withmethacylic acid in the presence of acetic acid to provide hydroxyphenylmethacrylate.

EXAMPLE 4 Polymer Synthesis

To a 500 mL, 3 neck round bottom flask equipped with a condenser,thermometer, magnetic stirrer and external oil heating bath, was addedthe following: 4-hydroxyphenyl methacrylate (HPhMA) (16.56 g, 0.093mol), methyl methacrylate (MMA) (15.54 g, 0.155 mol), and tert-butylacrylate (TBA) (7.95 g, 0.062 mol). Methanol (270 mL) was added and theresulting solution heated to reflux (67° C.). Once at reflux, a solutionof initiator 2,2′-azobis-2,4-dimethylpentanenitrile (1.54 g, 0.006 mol)in methanol (17.5 mL). The solution was held for 2 hours at reflux,after which another charge of initiator was added to the flask (0.77 g,0.003 mol) in methanol (9 mL). The solution was held at reflux for 16hours. After cooling, the polymer solution in methanol was washed withheptanes (3×300 mL). The solution was concentrated on a rotaryevaporator to remove residual heptanes and then precipitated into DIwater (2 liters). The wet cake was air dried for 24 hours and then driedat 60° C. under vacuum for 18 hours. The yield was 90%.

EXAMPLE 5-6 Additional Polymer Synthesis

Additional HPhMA:MMA:TBA terpolymers were prepared by the procedures ofExample 4 above, but varying amount of monomers employed. In Table 1below which follows Example 9, the ratio of each of the monomer units(as determined by ¹³C NMR analysis of the formed polymer), weightaverage molecular weight (Mw) and polydispersity (PD) are provided forthe HPhMA:MMA:TBA terpolymers formed in Examples 5 and 6.

EXAMPLES 7 Additional Polymer Synthesis

To a 500 mL, 3 neck round bottom flask equipped with a condenser,thermometer, magnetic stirrer and external oil heating bath, was addedthe following: 4-hydroxyphenyl methacrylate (HPhMA) (27.94 g, 0.157mol), styrene (STY) (10.89 g, 0.105 mol), and tert-butyl acrylate (TBA)(11.17 g, 0.087 mol). Methanol (340 mL) was added and the resultingsolution heated to reflux (67° C.). Once at reflux, a solution ofinitiator 2,2′-azobis-2,4-dimethylpentanenitrile (1.73 g, 0.007 mol) inmethanol (20 mL). The solution was held for 2 hours at reflux, afterwhich another charge of initiator was added to the flask (0.87 g, 0.004mol) in methanol (10 mL). The solution was held at reflux for 16 hours.After cooling, the polymer solution in methanol was washed with heptanes(3×300 mL). The solution was concentrated on a rotary evaporator toremove residual heptanes an then precipitated into DI water (2.5liters). The wet cake was air dried for 24 hours and then dried at 60°C. under vacuum for 18 hours. The yield was 90%.

EXAMPLE 8-9 Additional Polymer Synthesis

Additional HPhMA:STY:TBA terpolymers were prepared by the procedures ofExample 7 above, but varying amount of monomers employed. In Table 1below, the ratio of each of the monomer units (as determined by ¹³C NMRanalysis of the formed polymer), weight average molecular weight (Mw)and polydispersity (PD) are provided for the HPhMA:STY:TBA terpolymersformed in Examples 8 and 9.

TABLE 1 Polymer Characterization Composition Example Polymer Description(13C-NMR) Mw PD 4 HPhMA/MMA/TBA 32/51/17 15400 2.7 5 HPhMA/MMA/TBA42/40/18 18300 2.9 6 HPhMA/MMA/TBA 55/27/18 20200 3.1 7 HPhMA/STY/TBA44/26/30 15300 2.6 8 HPhMA/STY/TBA 50/34/16 13100 2.3 9 HPhMA/STY/TBA54/33/13 13700 2.3

EXAMPLE 10 Dissolution Rate Studies

Polymers of the above examples were coated to approximately equal dried(soft bake) coating layers over a wafer substrate. Dissolution rateswere measured of those polymer coating layers with a 0.26 N alkalineaqueous developer. Dissolution rates are set forth in Table 2 below.Measured Tg values also are set forth in Table 2 below.

TABLE 2 Polymer Characterization OD at DR (A/sec) in Tg 248 nm 0.26 NExample Polymer Description (° C.) (1/μ) TMAH 4 HPhMA/MMA/TBA 116 0.531.2 5 HPhMA/MMA/TBA 125 0.67 16.6 6 HPhMA/MMA/TBA 130 0.78 115 7HPhMA/STY/TBA 106 0.63 0.36 8 HPhMA/STY/TBA 117 0.73 2.0 9 HPhMA/STY/TBA122 0.79 7.8

EXAMPLE 11 Optical Density Evaluations

Polymers of the above examples were coated to approximately equal dried(soft bake) one micron thick coating layers over a wafer substrate.Polymer layer thickness was measured by ellipsometry. The absorbance ofthe films on quartz was determined by UV spectrophotometry. Theabsorbance was measured against a blank quartz wafer. Optical density(OD) was calculated at 248 nm using thickness and absorbancemeasurements. Measured OD values are set forth in Table 3 below.

TABLE 3 Polymer Characterization OD at 248 nm Example PolymerDescription (1/μ) 4 HPhMA/MMA/TBA 0.53 5 HPhMA/MMA/TBA 0.67 6HPhMA/MMA/TBA 0.78 7 HPhMA/STY/TBA 0.63 8 HPhMA/STY/TBA 0.73 9HPhMA/STY/TBA 0.79

EXAMPLE 12 Photoresist Preparation and Lithographic Processing

A photoresist of the invention is prepared by admixing the followingcomponents in the specified amounts:

Resist component Amount Resin to provide 11.4 wt. % total solids liquidformulation Photoacid generator 3.5 wt. % of resin component Basicadditive 0.1 wt. % of polymer Surfactant 0.05 wt. % of total solids.

In that resist, the polymer is a HPhMA:MMA:TBA terpolymer prepared asdescribed in Example 4. The photoacid generator of the resist isdi-tertbutylphenyliodonium camphorsulfonate. The basic additive is thelactate salt of tetremethylammonium hydroxide. The surfactant is thecommercially available material sold under the name R08. The solvent isethyl lactate.

That photoresist composition is spin coated onto 200 mm silicon wafershaving a coating of an organic antireflective composition. The appliedphotoresist later is soft-baked at 90° C. for 60 seconds and exposedthrough a photomask to 248 nm radiation. The exposed resist coatinglayer is then baked at 100° C. for 90 seconds and developed using analkaline aqueous developer.

EXAMPLE 13 Additional Photoresist Preparation and LithographicProcessing

A photoresist of the invention is prepared by admixing the followingcomponents in the specified amounts:

Resist component Amount Resin to provide 11.4 wt. % total solids liquidformulation Photoacid generator 3.53 wt. % of resin component Basicadditive 0.12 wt. % of polymer Surfactant 0.05 wt. % of total solids.

In that resist, the polymer was a HPhMA:STY:TBA terpolymer prepared asdescribed in Example 7. The photoacid generator of the resist isdi-tertbutylphenyliodonium camphorsulfonate. The basic additive is thelactate salt of tetremethylammonium hydroxide. The surfactant is thecommercially available material sold under the name R08. The solvent isethyl lactate.

That photoresist composition is spin coated onto 200 mm silicon wafershaving a coating of an organic antireflective composition. The appliedphotoresist later is soft-baked at 90° C. for 60 seconds and exposedthrough a photomask to 248 nm radiation. The exposed resist coatinglayer is then baked at 100° C. for 90 seconds and developed using analkaline aqueous developer.

What is claimed is:
 1. A method of forming a positive photoresist reliefimage, comprising: (a) applying on a substrate a layer of a photoresistcomprising a photoactive component and a resin, the resin comprises astructure of the following formula

wherein each Z is the same or different bridge unit; X comprises one ormore alkyl, oxygen or sulfur atoms; each R¹ is the same or differentnon-hydrogen substituent; and m is an integer of from zero to 4; AL is amoiety that comprises a photoacid-labile group; Y is a moiety that isdistinct from the spaced phenolic group or moiety that comprises AL, andY is selected from the group consisting of phenyl; phenyl substitutedwith halogen, cyano, alkyl or alkoxy; and an ester that does not undergoa photoacid-indueed cleavage reaction during exposing and developing ofthe photoresist layer; a, b and c are mole percents of the respectivepolymer units based on total repeat units in the polymer and a, b and care each greater than zero; and (b) exposing and developing thephotoresist layer to yield a relief image.
 2. The method of claim 1wherein X consists essentially of one or more alkyl or oxygen atoms. 3.The method of claim 1 wherein the resin comprises a structure of thefollowing formula

each R is the same or different and is hydrogen or optionallysubstituted alkyl; each Z is the same or different bridge unit; Xcomprises one or more alkyl, oxygen or sulfur atoms; each R¹ is the sameor different non-hydrogen substituent; m is an integer of from zero to4; P is a moiety that provides a photoacid-labile ester; Y is a moietythat is distinct from the spaced phenolic group or moiety that comprisesP, and Y is selected from the group consisting of phenyl; phenylsubstituted with halogen, cyano, alkyl or aikoxy; and an ester that doesnot undergo a photoacid-induced cleavage reaction during exposing anddeveloping of the photoresist layer; and a, b and c are mole percents ofthe respective polymer units based on total repeat units in the polymerand are each greater than zero.
 4. The method of claim 3 wherein Xconsists essentially of one or more alkyl or oxygen atoms.
 5. The methodof claim 1 wherein the resin comprises polymerized units ofhydroxyphenylmethacrylate; methyl methacrylate; and tert-butyl acrylate.6. The method of claim 1 wherein the resin comprises polymerized unitsof hydroxyphenylmethacrylate; styrene; and tert-butyl acrylate.
 7. Themethod of claim 1 wherein ions are applied to the substrate after thephotoresist relief image is formed.